Present invention relates to a multi-linked working boom for a working machine, where the boom carries at the outer end a hydraulically manoeuvrable working tool, especially rock drilling equipment, and comprises a first pair of hydraulically manoeuvrable link arms, which are connected to the working machine, and a second pair of hydraulically manoeuvrable link arms, which connect the working tool to the first pair of link arms.
An arrangement of the afore-mentioned kind is shown in SE-B 449 882. There is shown a working tool in the form of a timber grab, where a bunch of timber logs are to be moved in one and the same direction from the collection location to the delivery location by movement of link arms of a working boom in one and the same vertical plane. In addition the working boom can be swung about an extra vertical axis of the working machine. The power means for swinging the working arms is operated with hydraulic oil supplied from the hydraulic system of the working machine. The working boom is shown in the form of a first and a second pair of link arms which serve to increase longitudinally the working area of the working boom via a series of successive link arms. The four link arms illustrated are pivotally mounted about their mutually parallel pivot axes by means of their respective hydraulic pressure cylinders. The working boom is adapted to be able to be supported against the ground by means of a support plate on the under side of the third link arm, reckoned from the working machine, in order thereby to unload via the outer link arms during an introductory timber transport phase portions of the load from the working boom to the ground. In this connection a support plate is arranged on the under side of the middle link of the loading boom. The support plate has however an exclusive function during said introductory transport phase.
Similar working booms are also shown in EP-A1-0 299 104 and in DE-C1 41 32 173 in connection with hydraulically swingable loading shovels, where the working booms are swung in a manner corresponding to the timber grab.